JPH09183760A - Production of acrylamide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent polymerization and material defects of acrylamide product when reaction is reopened using a reaction solution by keeping the reaction solution in a stable state when acrylonitrile is subjected to hydration reaction to produce acrylamide. SOLUTION: Acrylonitrile is subjected to hydration reaction in the presence of a copper catalyst (e.g. reduced copper) in the absence of oxygen at 50-200 deg.C under ordinary pressure to 2Mpa pressure to provide the objective acrylamide. In the reaction, the acrylonitrile concentration in liquid phase component of the reaction solution in stopping the reaction is kept to >=1.0wt.%, most preferably >=8.0wt.% at 10-50 deg.C in an inert gas. Thereby, since the reaction solution is not deteriorated and oligomer is not produced, clogging of a filter for separating the copper catalyst and unexpected polymerization reaction in a reactor are not carried out in a reaction solution obtained after reopening of the reaction.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing acrylamide. Specifically, the reaction solution when acrylonitrile is hydrated to acrylamide is stored in a stable state, and the polymerization is prevented when the reaction is restarted using the reaction solution, and the quality defect of the product acrylamide is prevented. The present invention relates to a method for producing acrylamide.

[0002]

2. Description of the Related Art The most common method for producing acrylamide is to obtain acrylamide as an aqueous solution by reacting acrylonitrile with water in the presence of a copper catalyst to carry out a hydration reaction. When carrying out this method industrially,
Usually, the continuous method is adopted. However, even when the continuous method is carried out, the reaction may be stopped regularly or temporarily due to an inspection of the production reaction facility or for some reason. The time from the stop of the reaction to the restart of the reaction varies depending on the circumstances, but is usually about 6 hours to 3 months. In this case, generally, the temperature of the reactor is lowered to stop the reaction, the reaction liquid in the reactor is once taken out, and when the reaction is started after inspection and the like, the reaction liquid is fed to the reactor again. A method of charging and starting the reaction is adopted.

[0003]

The reaction liquid taken out of the reactor is generally stored and handled in an inert gas atmosphere so that the contained copper catalyst is not deactivated. However, even during this storage, a part of the reaction solution deteriorates to generate oligomers, etc., and as a result, in the reaction solution obtained after the restart of the reaction, the filter for separating the copper catalyst may be clogged, or Therefore, there is a problem that a polymerization reaction occurs suddenly in the reactor. Further, there is a problem that the quality of the product acrylamide obtained by using the reaction solution is deteriorated.

[0004]

As a result of various studies to solve the above problems, the present inventors have found that the acrylonitrile concentration in the reaction liquid during the reaction is kept above a certain value. The inventors have found that the object of can be achieved and reached the present invention. That is, the gist of the present invention is, in a method of continuously producing acrylamide by hydrating acrylonitrile in the presence of a copper catalyst, the concentration of acrylonitrile in the liquid phase component of the reaction liquid when the reaction is stopped is 1.0
A method for producing acrylamide is characterized in that the reaction solution is used as it is as a reaction raw material solution when the reaction is restarted by maintaining the content at not less than wt%. Further, in the method for storing an acrylamide reaction solution obtained by hydrating acrylonitrile in the presence of a copper catalyst, the concentration of acrylonitrile in the liquid phase component of the acrylamide reaction solution is 1.
A method for storing an acrylamide reaction solution is characterized in that the content is maintained at 0% by weight or more.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The reaction conditions in the method for producing acrylamide targeted by the present invention are a method for obtaining an aqueous solution of acrylamide by reacting acrylonitrile with water in the presence of a copper catalyst,
For example, it is described in JP-B-55-35376.

As the copper catalyst, metallic copper; Ullmann copper; Raney copper; reduced copper; copper oxide; copper sulfate, copper nitrate, copper phosphate,
Examples thereof include copper salts of inorganic acids such as copper thiocyanate and copper chloride; copper salts of organic acids such as fatty acid copper. Further, in order to improve the catalytic performance, Cr, Nl,
Co, Mo, Zn, Fe, W, Pd, Ti, Pt, S
Metals such as i, Rh, Rb, and V may be added as they are, or oxides or sulfides thereof may be added, or copper may be bonded to them to form a composite compound. Also,
These catalysts may be supported on a carrier such as asbestos, silica gel, graphite, carbon black or ion exchange resin.

The hydration reaction of acrylonitrile is continuously carried out in a fixed bed or a suspension bed in the presence of the above copper catalyst. The reaction temperature is usually 50 to 200 ° C., preferably 70
１５０150 ° C. Reaction pressure is usually atmospheric pressure to 2MP
a, preferably atmospheric pressure to 0.6 PMa. In addition, the reaction system may be in the absence of oxygen in order to prolong the life of the catalyst. Water and acrylonitrile, which are raw materials, are continuously supplied to the reactor, stay in the reactor for a predetermined time, and are continuously extracted as a reaction liquid containing unreacted raw materials. The reactor may be a single stage or a multistage reaction using a plurality of reactors of about 2 to 5 stages.

The concentration of acrylonitrile in the reactor during the reaction is not particularly limited, and it may vary depending on the supply ratio of the starting acrylonitrile and water, the reaction conversion rate, and the number of stages of the reactor when the reaction is carried out in multiple stages. If the concentration of acrylonitrile is too low, the reaction rate may be lowered. Therefore, the concentration of acrylonitrile in the liquid phase component of the reaction liquid at the outlet of the reactor is usually 1% by weight or more, preferably 3% by weight or more, It is preferably 4 to 8% by weight. The amount of water used may be equal to or higher than the stoichiometric amount of acrylonitrile, but since the solubility of acrylonitrile in water is not very large and it is difficult to carry out a homogeneous liquid phase reaction, it is usually several times the stoichiometric amount of acrylonitrile. Used several tens of times. In addition, alcohols such as methanol and ethanol can be used together depending on the case. Since the acrylamide produced is highly polymerizable, a polymerization inhibitor such as hydroquinone or t-butylcatechol may be used in the reaction.

The method of stopping the reaction as described above is generally carried out by the following method. First, the temperature inside the reactor is usually lower than 50 ° C., preferably at room temperature (temperature) by stopping the supply of acrylonitrile and water to the reactor and the withdrawal of the reaction liquid from the reactor, and stopping the heating of the reactor. 25 ℃). The temperature inside the reactor is 10 ℃
It is preferable that this is the case. Then, the residual reaction liquid containing the catalyst in the reactor is withdrawn into a tank previously replaced with an inert gas such as nitrogen. Further, in the case of an emergency stop, a method of holding the residual reaction liquid as it is in the reactor is also common. Furthermore, when stopping the withdrawal of the reaction liquid from the reactor, the reaction liquid withdrawn from the reactor is circulated by a method such as bypassing the raw material supply pipe to the reactor and the reaction liquid withdrawal pipe from the reactor. You may employ the method of making.

The feature of the present invention is that the concentration of acrylonitrile in the liquid phase component of the reaction solution when the above reaction is stopped is 1.0% by weight or more, preferably 2.0% by weight or more, more preferably 4.0% by weight. % Or more, most preferably 8.0% by weight or more. This not only allows the reaction solution to be stored in a stable state, but is also good in preventing sudden polymerization reactions that occur when the reaction is restarted using the solution that has been stored for a certain period of time, and in preventing quality defects of the product acrylamide. Is. The acrylonitrile concentration in the liquid phase component of the reaction solution means a concentration based on the liquid phase component obtained by filtering out the solid catalyst component in the reaction liquid.

When the acrylonitrile concentration is stored at less than 1.0% by weight, the reaction solution is easily denatured to form oligomers, etc. As a result, in the reaction solution obtained after the reaction is restarted, the filter for separating the copper catalyst is clogged. Or in some cases a polymerization reaction occurs suddenly in the reactor. Although the mechanism of action of the present invention is not clear, in the conventional method of storing a reaction solution having a low acrylonitrile concentration, the acrylamide formed on the catalyst in the reaction solution is concentrated and an oligomer or the like is easily formed. On the other hand, in the present invention, it is presumed that the concentration of acrylamide is suppressed and reduced, and oligomers are less likely to be produced. The upper limit of the concentration of acrylonitrile in the residual reaction solution is not particularly limited, but if the concentration is too high, undesired reactions may occur, so it is usually 50% by weight or less.

Further, when the reaction is stopped, the temperature of the reaction solution is usually 50 ° C. or lower to about room temperature. Even in such a temperature range, acrylonitrile and water in the reaction solution slightly react, and Results The acrylonitrile concentration decreases with time. Therefore, the acrylonitrile concentration is 1.0% by weight or more, preferably 2.0% by weight or more, more preferably 4.0% by weight or more, and most preferably 8.0% by weight or more.
Acrylonitrile needs to be added as needed to maintain the content at more than wt%. As a method for adjusting the acrylonitrile concentration of this residual reaction liquid, the acrylonitrile concentration of the reaction liquid is measured continuously or intermittently, and acrylonitrile is added when the concentration becomes a certain value or less, acrylonitrile at the initial stage of reaction termination. Is added in a large amount so that the acrylonitrile concentration is maintained at a predetermined value or more even if the acrylonitrile is consumed during the subsequent storage. Further, a method of increasing the acrylonitrile concentration in the reaction liquid by lowering the reaction temperature without stopping the supply of the raw material acrylonitrile during the reaction and stopping the withdrawal of the reaction liquid may be used. The addition of acrylonitrile may be performed once or dividedly in several times, or the above methods may be appropriately combined.

The reaction is usually restarted by the following method. First, the above-mentioned residual reaction liquid is supplied to the reactor whose nitrogen has been replaced at a low temperature such as room temperature, and then the supply of acrylonitrile and water is started while gradually increasing the temperature. Further, when the method of holding the reaction liquid as it is in the reactor as described above is adopted, the operation of supplying the reaction liquid to the reactor is unnecessary. In the present invention, 1 after restarting the reaction
It is necessary that the reaction be carried out well without causing clogging in the reactor due to formation of oligomers for a week.

[0014]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the examples as long as the gist thereof is not exceeded. Example 1 A reduced copper catalyst was charged into a reactor (90 parts by volume) equipped with a filter for separating the catalyst inside. There, 35
A 5% by weight aqueous solution of acrylonitrile was continuously supplied at 5 parts by volume / hr to suspend the reduced copper catalyst at a reaction temperature of 100.
A catalytic hydration reaction was carried out under the reaction conditions of ° C and a reaction pressure of 0.4 MPa, and a reaction liquid consisting of acrylonitrile, acrylamide and water was continuously extracted at 5 parts by volume / hr.
The extracted reaction liquid was subjected to heat treatment to remove acrylonitrile and water and concentrated to obtain an about 50 wt% acrylamide aqueous solution, which was treated with a cation exchange resin to continuously obtain product acrylamide.

After carrying out the continuous reaction for 1 month by the above method, the reaction was stopped by stopping the supply of the raw material acrylonitrile aqueous solution and stopping the heating of the reactor to lower its temperature (final Reactor temperature: 3
5 ° C). The acrylonitrile concentration in the reaction solution containing the copper catalyst immediately after the termination was 4.0%. Further, when the temperature in the reactor decreased to 50 ° C., a predetermined amount of acrylonitrile was added to adjust the acrylonitrile concentration in the reaction solution to 9.0.
% By weight. Next, while replacing the system with nitrogen gas,
The reaction liquid in the reactor was extracted into a nitrogen-containing storage tank, and this was stored at room temperature for 2 weeks. At the time of extraction, a predetermined amount of acrylonitrile was further added in consideration of consumption of acrylonitrile during storage, and the acrylonitrile concentration was set to 12.0% by weight. The acrylonitrile concentration after storage for 2 weeks was 5.8% by weight. The reaction solution was returned to the reactor and the reaction was restarted. Even one month after the restart, the reaction state was good, and the filter in the reactor was not clogged.

Example 2 When the temperature of the reactor reached 50 ° C. when the reaction was stopped, the addition of acrylonitrile was not performed, and the acrylonitrile concentration after the addition of acrylonitrile during withdrawal to the storage tank was measured. The same procedure as in Example 1 was carried out except that the amount was 8.0% by weight, and the acrylonitrile concentration after storage for 2 weeks was 2.2% by weight. The reaction solution was returned to the reactor and the reaction was restarted. Even one month after the resumption, the reaction state was good, and clogging of the filter in the reactor due to oligomer formation was not observed.

Example 3 Except that acrylonitrile was not added at the time of stopping the reaction and that the acrylonitrile concentration after addition of acrylonitrile at the time of withdrawing to the storage tank was 5.0% by weight. When I did the same thing, 2
The acrylonitrile concentration after storage for a week was 1.0% by weight. When the reaction solution was returned to the reactor and the reaction was restarted, the reaction state for 1 week after the restart of the reaction was good. Comparative Example 1 When the reaction liquid obtained in Example 2 was stored at room temperature (25 ° C.) for 1 month, the acrylonitrile concentration was 0.5% by weight. When the reaction solution was returned to the reactor and the reaction was restarted, the filter was clogged from the beginning after the reaction was restarted, and normal continuous operation was impossible. Comparative Example 2 When the reaction solution obtained in Example 2 was stored at 40 ° C. for 1 week, the acrylonitrile concentration was 0.8% by weight.
When the reaction solution was returned to the reactor and the reaction was restarted, the filter was clogged from the beginning after the reaction was restarted, and normal continuous operation was impossible. Reference Experiment (Quality Evaluation of Product Acrylamide) In the same manner as in Example 2, the acrylonitrile concentration was 7.
A reaction liquid containing 2% by weight of a copper catalyst was prepared. Stirrer,
After replacing the inside of a glass flask having an internal volume of 1 liter equipped with a thermometer, a nitrogen sealing device and a reflux condenser with nitrogen gas, 700 mL of the above reaction solution was charged. Immerse this glass flask in a water bath, and under a nitrogen gas atmosphere,
Stirring was continued at each constant temperature of 0 and 40 ° C. A part of the reaction solution was taken out at regular intervals, and the acrylonitrile concentration and the solubility of the methanol solution, which is an index of the water-soluble polymer, were measured. The acrylonitrile concentration was measured by gas chromatography (column: chromosorb-101, column length 2 m, column temperature 170 ° C). To dissolve a methanol solution, dilute 5 g of the sample to 50 mL with methanol,
The transmittance at 650 nm was measured with a spectrophotometer using a 50 mm glass cell. The analysis results are shown in Table 1. In the table, the higher the value of methanol solubility, the better quality product acrylamide can be obtained. In the present invention, the solubility value of the methanol solution needs to be 99.0% or more. 9
If the value is less than 9.0%, the quality of the product acrylamide becomes poor because it contains oligomers and polymers.

[Table 1]

[0018]

EFFECTS OF THE INVENTION According to the present invention, the reaction liquid obtained by hydrating acrylonitrile to acrylamide can be stored in a stable state. Also, after the reaction is stopped, polymerization is prevented when the reaction is restarted using the reaction solution stored for a certain period,
Prevention of quality defects of product acrylamide is achieved.

Claims (17)

[Claims] 1. A method for continuously producing acrylamide by hydrating acrylonitrile in the presence of a copper catalyst, wherein the concentration of acrylonitrile in the liquid phase component of the reaction solution when the reaction is stopped is 1.0% by weight or more. And the reaction solution is used as a reaction raw material solution when the reaction is restarted. 2. The method for producing acrylamide according to claim 1, wherein the concentration of acrylonitrile in the liquid phase component of the reaction liquid when the reaction is stopped is maintained at 2.0% by weight or more. 3. The temperature of the reaction solution when the reaction is stopped is 10 ° C.
The method for producing acrylamide according to claim 1, wherein the method is maintained at 50 ° C or higher and lower than 50 ° C. 4. The method for producing acrylamide according to claim 1, wherein the reaction solution when the reaction is stopped is held in an inert gas. 5. The method for producing acrylamide according to claim 1, wherein the reaction liquid when the reaction is stopped is held in a reactor for hydration reaction. 6. The acrylonitrile concentration of the reaction solution when the reaction is stopped is measured continuously or intermittently, and the concentration is 1.0.
The method for producing acrylamide according to claim 1, wherein acrylonitrile is added when the content of the acrylamide becomes less than wt%. 7. A large amount of acrylonitrile is added to the reaction solution when the reaction is stopped so that the concentration of the reaction solution when the reaction is restarted is 1.0 wt% or more. The method for producing acrylamide according to claim 1, wherein 8. The reaction is stopped by lowering the reaction temperature without stopping the supply of the raw material acrylonitrile during the hydration reaction, and stopping the withdrawal of the reaction solution, so that the concentration of acrylonitrile is 1.0% by weight or more. The method for producing acrylamide according to claim 1, characterized in that 9. A method for supplying acrylonitrile and water while gradually increasing the temperature, after supplying the reaction raw material liquid at the time of restarting the reaction to a reactor whose nitrogen has been replaced at 10 ° C. or higher and lower than 50 ° C. The method for producing acrylamide according to claim 1, wherein 10. The method for producing acrylamide according to claim 1, wherein the hydration reaction is carried out at 50 to 200 ° C. 11. The method for producing acrylamide according to claim 1, wherein the hydration reaction is performed at atmospheric pressure to 2 MPa. 12. The method for producing acrylamide according to claim 1, wherein the hydration reaction is carried out in the absence of oxygen. 13. A method for storing an acrylamide reaction solution obtained by hydrating acrylonitrile in the presence of a copper catalyst, wherein the concentration of acrylonitrile in the liquid phase component of the acrylamide reaction solution is maintained at 1.0% by weight or more. A method for storing an acrylamide reaction solution, which comprises: 14. The method for preserving an acrylamide reaction solution according to claim 13, wherein the concentration of acrylonitrile in the liquid phase component of the acrylamide reaction solution is maintained at 2.0% by weight or more. 15. The method for measuring acrylonitrile concentration in a liquid phase component of an acrylamide reaction solution continuously or intermittently, and adding acrylonitrile when the concentration becomes less than 1.0% by weight. 13. The method for storing the acrylamide reaction solution according to item 13. 16. A large amount of acrylonitrile is added to the acrylamide reaction solution when the reaction is stopped in the initial stage of the reaction stop so that the concentration of the reaction solution when the reaction is restarted is 1.0% by weight or more. The method for storing the acrylamide reaction solution according to claim 13. 17. The reaction is stopped by lowering the reaction temperature without stopping the supply of the raw material acrylonitrile during the hydration reaction, and stopping the withdrawal of the reaction solution, so that the concentration of acrylonitrile is 1.0% by weight or more. The method for storing an acrylamide reaction solution according to claim 13, characterized in that